OK, let's work through this together. We're starting with 90 and we're going to multiply it by 241, which means we add 90 to itself 241 times.
Step 1: 0 + 90 = 90
Step 2: 90 + 90 = 180
Step 3: 180 + 90 = 270
Step 4: 270 + 90 = 360
Step 5: 360 + 90 = 450
Step 6: 450 + 90 = 540
Step 7: 540 + 90 = 630
Step 8: 630 + 90 = 720
Step 9: 720 + 90 = 810
Step 10: 810 + 90 = 900
Step 11: 900 + 90 = 990
Step 12: 990 + 90 = 1080
Step 13: 1080 + 90 = 1170
Step 14: 1170 + 90 = 1260
Step 15: 1260 + 90 = 1350
Step 16: 1350 + 90 = 1440
Step 17: 1440 + 90 = 1530
Step 18: 1530 + 90 = 1620
Step 19: 1620 + 90 = 1710
Step 20: 1710 + 90 = 1800
Step 21: 1800 + 90 = 1890
Step 22: 1890 + 90 = 1980
Step 23: 1980 + 90 = 2070
Step 24: 2070 + 90 = 2160
Step 25: 2160 + 90 = 2250
Step 26: 2250 + 90 = 2340
Step 27: 2340 + 90 = 2430
Step 28: 2430 + 90 = 2520
Step 29: 2520 + 90 = 2610
Step 30: 2610 + 90 = 2700
Step 31: 2700 + 90 = 2790
Step 32: 2790 + 90 = 2880
Step 33: 2880 + 90 = 2970
Step 34: 2970 + 90 = 3060
Step 35: 3060 + 90 = 3150
Step 36: 3150 + 90 = 3240
Step 37: 3240 + 90 = 3330
Step 38: 3330 + 90 = 3420
Step 39: 3420 + 90 = 3510
Step 40: 3510 + 90 = 3600
Step 41: 3600 + 90 = 3690
Step 42: 3690 + 90 = 3780
Step 43: 3780 + 90 = 3870
Step 44: 3870 + 90 = 3960
Step 45: 3960 + 90 = 4050
Step 46: 4050 + 90 = 4140
Step 47: 4140 + 90 = 4230
Step 48: 4230 + 90 = 4320
Step 49: 4320 + 90 = 4410
Step 50: 4410 + 90 = 4500
Step 51: 4500 + 90 = 4590
Step 52: 4590 + 90 = 4680
Step 53: 4680 + 90 = 4770
Step 54: 4770 + 90 = 4860
Step 55: 4860 + 90 = 4950
Step 56: 4950 + 90 = 5040
Step 57: 5040 + 90 = 5130
Step 58: 5130 + 90 = 5220
Step 59: 5220 + 90 = 5310
Step 60: 5310 + 90 = 5400
Step 61: 5400 + 90 = 5490
Step 62: 5490 + 90 = 5580
Step 63: 5580 + 90 = 5670
Step 64: 5670 + 90 = 5760
Step 65: 5760 + 90 = 5850
Step 66: 5850 + 90 = 5940
Step 67: 5940 + 90 = 6030
Step 68: 6030 + 90 = 6120
Step 69: 6120 + 90 = 6210
Step 70: 6210 + 90 = 6300
Step 71: 6300 + 90 = 6390
Step 72: 6390 + 90 = 6480
Step 73: 6480 + 90 = 6570
Step 74: 6570 + 90 = 6660
Step 75: 6660 + 90 = 6750
Step 76: 6750 + 90 = 6840
Step 77: 6840 + 90 = 6930
Step 78: 6930 + 90 = 7020
Step 79: 7020 + 90 = 7110
Step 80: 7110 + 90 = 7200
Step 81: 7200 + 90 = 7290
Step 82: 7290 + 90 = 7380
Step 83: 7380 + 90 = 7470
Step 84: 7470 + 90 = 7560
Step 85: 7560 + 90 = 7650
Step 86: 7650 + 90 = 7740
Step 87: 7740 + 90 = 7830
Step 88: 7830 + 90 = 7920
Step 89: 7920 + 90 = 8010
Step 90: 8010 + 90 = 8100
Step 91: 8100 + 90 = 8190
Step 92: 8190 + 90 = 8280
Step 93: 8280 + 90 = 8370
Step 94: 8370 + 90 = 8460
Step 95: 8460 + 90 = 8550
Step 96: 8550 + 90 = 8640
Step 97: 8640 + 90 = 8730
Step 98: 8730 + 90 = 8820
Step 99: 8820 + 90 = 8910
Step 100: 8910 + 90 = 9000
Step 101: 9000 + 90 = 9090
Step 102: 9090 + 90 = 9180
Step 103: 9180 + 90 = 9270
Step 104: 9270 + 90 = 9360
Step 105: 9360 + 90 = 9450
Step 106: 9450 + 90 = 9540
Step 107: 9540 + 90 = 9630
Step 108: 9630 + 90 = 9720
Step 109: 9720 + 90 = 9810
Step 110: 9810 + 90 = 9900
Step 111: 9900 + 90 = 9990
Step 112: 9990 + 90 = 10080
Step 113: 10080 + 90 = 10170
Step 114: 10170 + 90 = 10260
Step 115: 10260 + 90 = 10350
Step 116: 10350 + 90 = 10440
Step 117: 10440 + 90 = 10530
Step 118: 10530 + 90 = 10620
Step 119: 10620 + 90 = 10710
Step 120: 10710 + 90 = 10800
Step 121: 10800 + 90 = 10890
Step 122: 10890 + 90 = 10980
Step 123: 10980 + 90 = 11070
Step 124: 11070 + 90 = 11160
Step 125: 11160 + 90 = 11250
Step 126: 11250 + 90 = 11340
Step 127: 11340 + 90 = 11430
Step 128: 11430 + 90 = 11520
Step 129: 11520 + 90 = 11610
Step 130: 11610 + 90 = 11700
Step 131: 11700 + 90 = 11790
Step 132: 11790 + 90 = 11880
Step 133: 11880 + 90 = 11970
Step 134: 11970 + 90 = 12060
Step 135: 12060 + 90 = 12150
Step 136: 12150 + 90 = 12240
Step 137: 12240 + 90 = 12330
Step 138: 12330 + 90 = 12420
Step 139: 12420 + 90 = 12510
Step 140: 12510 + 90 = 12600
Step 141: 12600 + 90 = 12690
Step 142: 12690 + 90 = 12780
Step 143: 12780 + 90 = 12870
Step 144: 12870 + 90 = 12960
Step 145: 12960 + 90 = 13050
Step 146: 13050 + 90 = 13140
Step 147: 13140 + 90 = 13230
Step 148: 13230 + 90 = 13320
Step 149: 13320 + 90 = 13410
Step 150: 13410 + 90 = 13500
Step 151: 13500 + 90 = 13590
Step 152: 13590 + 90 = 13680
Step 153: 13680 + 90 = 13770
Step 154: 13770 + 90 = 13860
Step 155: 13860 + 90 = 13950
Step 156: 13950 + 90 = 14040
Step 157: 14040 + 90 = 14130
Step 158: 14130 + 90 = 14220
Step 159: 14220 + 90 = 14310
Step 160: 14310 + 90 = 14400
Step 161: 14400 + 90 = 14490
Step 162: 14490 + 90 = 14580
Step 163: 14580 + 90 = 14670
Step 164: 14670 + 90 = 14760
Step 165: 14760 + 90 = 14850
Step 166: 14850 + 90 = 14940
Step 167: 14940 + 90 = 15030
Step 168: 15030 + 90 = 15120
Step 169: 15120 + 90 = 15210
Step 170: 15210 + 90 = 15300
Step 171: 15300 + 90 = 15390
Step 172: 15390 + 90 = 15480
Step 173: 15480 + 90 = 15570
Step 174: 15570 + 90 = 15660
Step 175: 15660 + 90 = 15750
Step 176: 15750 + 90 = 15840
Step 177: 15840 + 90 = 15930
Step 178: 15930 + 90 = 16020
Step 179: 16020 + 90 = 16110
Step 180: 16110 + 90 = 16200
Step 181: 16200 + 90 = 16290
Step 182: 16290 + 90 = 16380
Step 183: 16380 + 90 = 16470
Step 184: 16470 + 90 = 16560
Step 185: 16560 + 90 = 16650
Step 186: 16650 + 90 = 16740
Step 187: 16740 + 90 = 16830
Step 188: 16830 + 90 = 16920
Step 189: 16920 + 90 = 17010
Step 190: 17010 + 90 = 17100
Step 191: 17100 + 90 = 17190
Step 192: 17190 + 90 = 17280
Step 193: 17280 + 90 = 17370
Step 194: 17370 + 90 = 17460
Step 195: 17460 + 90 = 17550
Step 196: 17550 + 90 = 17640
Step 197: 17640 + 90 = 17730
Step 198: 17730 + 90 = 17820
Step 199: 17820 + 90 = 17910
Step 200: 17910 + 90 = 18000
Step 201: 18000 + 90 = 18090
Step 202: 18090 + 90 = 18180
Step 203: 18180 + 90 = 18270
Step 204: 18270 + 90 = 18360
Step 205: 18360 + 90 = 18450
Step 206: 18450 + 90 = 18540
Step 207: 18540 + 90 = 18630
Step 208: 18630 + 90 = 18720
Step 209: 18720 + 90 = 18810
Step 210: 18810 + 90 = 18900
Step 211: 18900 + 90 = 18990
Step 212: 18990 + 90 = 19080
Step 213: 19080 + 90 = 19170
Step 214: 19170 + 90 = 19260
Step 215: 19260 + 90 = 19350
Step 216: 19350 + 90 = 19440
Step 217: 19440 + 90 = 19530
Step 218: 19530 + 90 = 19620
Step 219: 19620 + 90 = 19710
Step 220: 19710 + 90 = 19800
Step 221: 19800 + 90 = 19890
Step 222: 19890 + 90 = 19980
Step 223: 19980 + 90 = 20070
Step 224: 20070 + 90 = 20160
Step 225: 20160 + 90 = 20250
Step 226: 20250 + 90 = 20340
Step 227: 20340 + 90 = 20430
Step 228: 20430 + 90 = 20520
Step 229: 20520 + 90 = 20610
Step 230: 20610 + 90 = 20700
Step 231: 20700 + 90 = 20790
Step 232: 20790 + 90 = 20880
Step 233: 20880 + 90 = 20970
Step 234: 20970 + 90 = 21060
Step 235: 21060 + 90 = 21150
Step 236: 21150 + 90 = 21240
Step 237: 21240 + 90 = 21330
Step 238: 21330 + 90 = 21420
Step 239: 21420 + 90 = 21510
Step 240: 21510 + 90 = 21600
Step 241: 21600 + 90 = 21690

So, 90*241 = 21690